Answer: Neither. It's an old wives tale, but most say you should water as soon as lights come on. Why? Nobody can tell me. They say you just should. You will never ever convince me until I see a side by side with at least 10 plants each.

Like Jerry and Opie have suggested, I'm pretty sure you're giving them too much to eat. If you have a ppm pen then you can tell me what I asked. Next time you mix up a batch of food stick your ppm first in your plain water, and then in the mixture. Let me know both numbers, and how often you are feeding. Oops, just reread, you said PH pen. Oh well, If you don't want to get something to measure PPM, then you need to be real careful when feeding, making sure you feed much less at first than you think you should. Slowly build up until you see the first signs of nute burn, which you already have. Jerry brings up watering and I don't know how you are doing there, but you should be watering only when the soil has almost completely dried out at the bottom of the pot. You can stick your finger down there or buy a $5 moisture meter. When I stick mine to the bottom and the needle nearly stays still, I know it's time. After doing that a few times, you'll just know about when to water based on the weight of the container and how much dirt has pulled away from the edges of the container.

If I remember correctly you said you mixed your dirt with some vast quantity of perlite. Perlite is good, and should be mixed into most soil IMO, but you usually want to put in about 20 or 30%. More is OK, but you'll need to check for watering more often.

PS, You have the honer of my only hit-free post of the day, so I'm hoping it made some sense. Time to fire up.